Solid state microelectromechanical system (MEMS) pressure sensors are well known. For example, U.S. Pat. No. 4,236,137 to Kurtz, et al. discloses a semiconductor pressure transducer. U.S. Pat. No. 5,156,052 to Johnson, et al. also discloses a solid state pressure transducer. U.S. Pat. No. 6,006,607 to Bryzek, et al. discloses a pressure sensor that uses a piezoresistive device. U.S. Pat. Nos. 5,178,016 and 6,093,579 also discloses solid state pressure sensors.
A well-known problem with prior art MEMS pressure sensors, which use piezoresistive devices formed into a thin silicon diaphragm, is pressure nonlinearity or PNL. The PNL is a function of the silicon diaphragm's deflection. The greater the diaphragm deflection, the greater degree of output nonlinearity, whether the piezoresistance is detected and measured as a voltage or current.
Output nonlinearity becomes more problematic in sensors that are intended to detect low pressures, e.g., pressures below 10 kPa. Since low pressure sensing devices require very thin silicon diaphragms, the diaphragm deflection in a thin diaphragm tends to aggravate the PNL in pressure sensors that are designed to measure low pressures. Another problem with thin silicon diaphragms is that they are fragile. A major challenge is to create a diaphragm to lower or reduce PNL while improving pressure sensitivity without increasing the die size for a low pressure sensor. A solid state piezoresistive pressure sensor that can be used at low pressures and which has an improved output linearity and which is more rugged and more sensitive than those in the prior art would be an improvement.